Sewage sludge biochar derived binder-free electrode for electrochemical advanced oxidation treatment

Electrochemical oxidation (EOX) is a widely implemented tertiary wastewater treatment technique for eliminating and mineralising complex organics. In the present investigation, a sewage sludge-derived biochar electrode was fabricated with a binder-free methodology and implemented as a cathode in EOX treatment for the degradation of methylene blue (MB). Sewage sludge biochar was mixed with sucrose in ratio of 2:1 and successively pyrolyzed at 180, 500, and 900 degrees C to form cathode. Through electrochemical characterization, synthesised biochar cathode demonstrated excellent current response and low charge transfer resistance, surpassing carbon felt and matching graphite plate electrodes. Use of biochar electrode as a cathode in EOX treatment resulted in MB removal of 96.05 +/- 1.33 % within 60 min of contact time at a neutral pH with an imposed current density of 10 mA/cm2 and NaCl dosing of 1 g/L. The MB degradation rate using biochar cathode was superior to other carbonaceous cathodes and Ti-based mixed metal oxide cathode, which was attributed to the in-situ H2O2 generation during the oxygen reduction reaction. Moreover, the biochar cathode-based EOX treatment achieved greater than 90 % MB removal efficiency for 22 continuous cycles, showcasing its longevity for practical applications. The cost of the sucrose-based biochar electrode was estimated to be INR 2.12/cm2 (equivalent to USD 0.025/cm2), which was comparable to commercially available carbon felt and 9-folds lesser than graphite plate. The investigation demonstrates sewage sludge-derived sucrose-based biochar monolith as a low-cost cathode in EOX treatment, aligning with the principles of circularity in wastewater management.